Heat streaks are surface defects which often occur in cold rolling of thin gauge steel strip. Rolling conditions influencing the heat streak formation have been investigated using the commercial rolling mills. The mechanism of heat streak formation was revealed by microscopic observation of work rolls and rolled strip surface, and by analysis of oil film conditions in contact arc using elastohydrodynamic lubrication theory.
The summaries are as follows;
(1) Grinding scratches on a work roll form heat streaks in each case of heavy reduction rolling, high speed rolling, rolling of hard meterial and cooling with an insufficient coolant flow rate.
(2) Grinding scratches extremely increase oil film pressure and temperature around the scratches. When the oil film breaks out due to the increase of pressure and temperature, heat streaks occur.
(3) Two effective countermeasures were obtained. The first is to control the size of roll surface defects under 3 μm, and the second is to use rolling oil of high boundary lubricity which can endure high pressure and temperature.
